Precise atmospheric trajectories including dynamic and photometric data on thirteen of the brightest Leonid fireballs have been determined from the double-station photographic observations of Leonid meteors during the ground-based expedition to China in 1998 November. The expedition was organized as a collaboration between the Dutch and Chinese Academy of Sciences and was supported by the Leonid multi-instrument aircraft campaign (MAC) program (Jenniskens and Butow, 1999). All data presented here were taken at Xinglong Observatory and at a remote station, Lin Ting Kou near Beijing, on the night of 1998 November 16/17. At the Xinglong station, photographic cameras were accompanied by an all-sky television camera equipped with an image intensifier and 15 mm fish-eye objective in order to obtain precise timings for all observed meteors up to magnitude +2. Whereas beginning heights of photographed meteors are all lower than 130 km, those observed by the all-sky television system are at -160 km, and for three brightest events, even > 180 km. Such high beginnings for meteors have never before been observed. We also obtained a precise dynamic single-body solution for the Leonid meteor 98003, including the ablation coefficient, which is an important material and structural quantity (0.16 s2 kn-2). From this and from known photometry, we derived a density of this meteoroid of 0.7 g/cm3. Also, all PE coefficients indicate that these Leonid meteors belonged to the fireball group IIIB, which is typical for the most fragile and weak interplanetary bodies. From a photometric study of the meteor lightcurves, we found two typical shapes of light curves for these Leonid meteors. (1997) Precisely reduced meteoroid trajectories and orbits from the 1995 Leonid meteor outburst. Planet. Space Sci. 45,853-856. CEPLECHA Z. (1987) Geometric, dynamic, orbital and photometric data on meteoroids from Dhotoeraohic fireball networks. Bull. Astron. Inst. -. Czech. 38,222-23i. Luminous efficiency based on photographic observations of the Lost City fireball and implications for the influx of interplanetary bodies onto Earth. Astron. Ashophys. 311,329-332.

Abstract— In this paper, we study the extremely high beginning parts of atmospheric trajectories of seven Leonid meteors recorded by sensitive TV systems equipped with image intensifiers up to apparent magnitude +6.5. For all seven cases, we observed comet‐like diffuse structures with sizes on the order of kilometers that developed quickly during the meteoroids' descent through the atmosphere. For the brightest event with a maximum absolute magnitude of −12.5, we observed an arc similar to a solar protuberance and producing a jet detectable several kilometers sideways from the brightest parts of the meteor head, and moving with a velocity over 100 km/s. These jets are common features for the seven studied meteors. Precise position in trajectory, velocity, and brightness at each point is available for all seven meteors, because of double‐station records on 85 km base‐line. When these meteoroids reached 130 km height, their diffuse structures of the radiation quickly transformed to the usual meteor appearance resembling moving droplets, and meteor trains started to develop. These meteor phenomena above 130 km were not recognized before our observations, and they cannot be explained by standard ablation theory.

We present the first measurements of the radiant and orbit of meteoroids that are part of the unusual Perseid activity called the ‘Perseid Filament’. This filament was encountered by Earth in the years before and after the return of the comet to perihelion in December of 1992. Between 1989 and 1996, there were brief meteor outbursts of near‐constant duration with a symmetric activity profile. In 1993, however, rates increased more gradually to the peak. That gradual increase is identified here as a separate dust component, which we call the ‘Nodal Blanket’. We find that the Nodal Blanket has a very small radiant dispersion. On the other hand, the Perseid Filament has a radiant that is significantly dispersed and systematically displaced by 0.3°. This dispersion implies that unusually high ejection velocities or planetary perturbations must have had time to disperse the stream. In both cases, one would expect a rapid dispersion of matter along the comet orbit. In order to explain the concentration of dust near the comet position, we propose a novel scenario involving long‐term accumulation in combination with protection of the region near the comet against close encounters with Jupiter due to librations of the comet orbit around the 1:11 mean‐motion resonance.

Abstract. 359 precisely reduced meteor orbits are presented that are the result of the Dutch Meteor Society's Photographic Meteor Survey in the period 1981 until 1993. Orbits include those of major and minor showers, doubling the number of known precise orbits of some meteor streams. From the spread in solutions of all possible sets of two photographic stations, we derive the measurement uncertainties from which we are able to calculate the intrinsic scatter in the Perseid meteor stream. The new Geminid orbits are compared to those obtained in similar surveys in the 1950's. This first measurement of the rate of change of Geminid orbits over time agrees well with model predictions.

Abstract-Seventy-five orbits of Leonid meteors obtained during the 1998 outburst are presented. Thirtyeight are precise enough to recognize significant dispersion in orbital elements. Results from the nights of 1998 November 16/17 and 17/18 differ, in agreement with the dominant presence of different dust components. The shower rate profile of 1998 November 16/17 was dominated by a broad component, rich in bright meteors. The radiant distribution is compact. The semimajor axis is conjined to values close to that of the parent comet, whereas the distribution of inclination has a central condensation in a narrow range. On the other hand, 1998 November 17/18 was dominated by dust responsible for a more narrow secondary peak in the flux curve. The declination of the radiant and the inclination of the orbit are more widely dispersed. The argument of perihelion, inclination, and the perihelion distance are displaced. These data substantiate the hypothesis that trapping in orbital resonances is important for the dynamical evolution of the broad component.